1. Field of the Invention
The present invention relates to an image forming apparatus and a gloss level control method, and more particularly, to an electrophotographic image forming apparatus that fixes toner image and a gloss level control method for applying to the image forming apparatus.
2. Description of the Related Art
In recent years, image forming apparatuses such as printers and copiers are required to provide image output of higher quality. One criterion for evaluating image quality is a gloss level of a printed image. Especially for a photograph or illustration, an image having high gloss level tends to be preferred.
Factors that control the gloss level of an image in an electrophotographic image forming apparatus are duration and/or temperature of fixing an unfixed toner image onto a sheet such as a paper sheet and OHP film as image carrier by a fixing unit. In other words, the factor is an amount of heat applied to a sheet during fixation. Depending on the amount of heat, melting condition of a toner and/or permeability of a toner into a sheet varies, which causes the gloss level of an image to vary. In general, the more the amount of applied heat increases, the higher gloss level an image has.
Choice of the gloss level of an image depends on a user's preference. Users are likely to want a high gloss level when outputting an image like a photograph or illustration. On the contrary, for business documents, many users prefer a low gloss level because it is difficult for the users to fill in a glossy document with a pen or pencil, for example. However, this is just a general trend, and a gloss level desired for an output image varies from user to user. Thus, there has been a need for an image forming apparatus that can provide an image gloss level that meets a user's request.
Conventionally, for realizing a gloss level desired by a user, there have been known an apparatus that is capable of performing a setting/change of the gloss level of an image according to a user's designation (see Japanese Laid-Open Patent Publication (Kokai) H06-202520, for example), and an apparatus that outputs an image with a gloss level appropriate for the type of the image determined by an image forming apparatus (see Japanese Laid-Open Patent Publication (Kokai) No. H09-160315, for example).
However, as the apparatus disclosed by the Japanese Laid-Open Patent Publication (Kokai) No. H09-160315 selects a gloss level by determining the type of an image for each page, originals including different types of images, e.g. characters and photographs, have different gloss levels from page to page. For this reason, the apparatus is inconvenient for a user who desires to have the same gloss level for an entire output bundle. The apparatus also indicates composition ratio of image types that constitute pages and allows a user to select a desired gloss level. With this apparatus, the user can perform a setting of the same gloss level for the entire output bundle, but the user has to set a gloss level based on the indicated composition ratio of image types by himself.
The apparatus disclosed by the Japanese Laid-Open Patent Publication (Kokai) No. H06-202520 has a drawback in that a user has to determine the ratio of images making up an original, e.g. characters and photographs, and set a gloss level on his own.